Apparatus for control of web tension in multicolor printing machines

ABSTRACT

An apparatus for damping of tensile stress variations and for control of the web tension on braked unwinding devices for webs of flexible material, as paper, plastic foils, and the like, which comprises a dancer roller disposed between a first feeding roller and a second feeding roller. The first feeding roller is arranged on the roller side and serves as a moment compensation device. The second feeding roller serves as a feeding device for the web. A gear is provided for driving the first feeding roller, and a slip coupling is operatively disposed between the first feeding roller and the gear.

United States Patent APPARATUS FOR CONTROL OF WEB TENSION IN MULTICOLORPRINTING MACHINES 1 Claim, I Drawing Fig.

US. Cl 242/75-43,

Int. Cl B65h 25/22 Field of Search 226/40, 41,

[56] References Cited UNITED STATES PATENTS 2,115,737 5/1938 Menschner226/44 X 3,326,436 6/1967 Huck 226/44 X Primary Examiner- Richard A.Schacher A!t0rneyEmest G. Montague ABSTRACT: An apparatus for damping oftensile stress variations and for control of the web tension on brakedunwinding devices for webs of flexible material, as paper, plasticfoils, and the like, which comprises a dancer roller disposed between afirst feeding roller and a second feeding roller. The first feedingroller is arranged on the roller side and serves as a momentcompensation device. The second feeding roller serves as a feedingdevice for the web. A gear is provided for driving the first feedingroller, and a slip coupling is operatively disposed between the firstfeeding roller and the gear.

PATENTED DEC 7|97| 3,625,447

NTO DIE H HA BY ATTORNEY.

APPARATUS FOR CONTROL OF WEB TENSION IN MULTICOLOR PRINTING MACHINES Thepresent invention relates to an apparatus for damping of tensile stressfluctuations and for control of the web tension on braked unrollingdevices for webs of flexible material, for instance, paper, plasticfilms, and the like, by means of a dancing roller, as set forth in thecopending patent application Ser. No. 709,108, filed Feb. 28, 1968, inwhich the dancing roller is disposed between two feeding rollers feedingto each other synchronously, the roller-side feeding roller of whichoperates as moment compensation device. By the roll-sided feeding rolleras a moment compensation device, the web is fed with a speed equal withthat of the dancing roller, as it is drawn from the latter by the otherfeeding roller into the working machine, so that the expansion of theweb depending upon the web tension causes a movement of the dancingroller during compensation with the expansion of the web occurring bythe mass of the dancing roller due to the web load, which movement ofthe dancing roller is exploited for the control of the braking of theroller and thereby of the web tension between the roller and the momentcompensation device.

This apparatus permits a control of the web tension with minimalmovements of the dancing roller, which do not require any more dampingand which bring about an extremely stable control of the median webtension between the roller and the moment compensation device. Extremeweb tension fluctuations are reliably equalized within the range betweenthe moment compensation device and the feeding roller following thedancing roller, if the web tension peaks between the roller and themoment compensation device do not lead in case of pull-sensitive webs toa web extension beyond the elastic range or even to a tearing of theweb. The disturbancefree feeding of pull-sensitive webs brings aboutcertain difficulties and cannot be obtained always under all occurringoperating conditions. A further drawback of this apparatus resides inthe fact that, for restarting after an emergency braking, as well asupon inserting a new web, particular measures must be taken in order torender ineflective, temporarily, the control. At first, the brake mustbe switched off, so that the roller can rotate freely, then thecounterpressure roller of the first feeding roller serving as a momentcompensation device must be lifted, so that the web can be fed to thesecond feeding roller or can be pulled taut and when it is retained inthe direction of movement forwardly, by the return rotation of theroller, the dancing roller is lifted into its normal position andthereafter the counterpressure roller is lowered again and the brake isagain switched on. The performance of these particular measures withmechanical means in the manner of a follow control requires a certainnot appreciable expenditure.

It is one object of the present invention to provide an apparatus fordamping of tensile stress fluctuations and for control of the webtensions of unrolling devices, wherein these drawbacks of the knownstructures are eliminated and the possibility is created to roll offmaterial with different security and expansion characteristics. In orderto obtain this end, the problem must be solved, to make variable theeffect of the moment compensation device on the web and the value of themoments to be compensated, respectively, so that web tensions which areextremely low, as well as median web tensions which surpass a settablelimit value between the roller and the moment compensation device movebeyond those and can influence the dancing roller directly for thepurpose of an accelerated control.

It is another object of the present invention to provide an apparatusfor damping of tensile stress fluctuations and for control of the webtension on braked unrolling devices, for webs of flexible material bymeans of a dancing roller, which is disposed between a feeding rollerserving as moment compensation device and a second feeding rollerserving the drive of the web, which is arranged in such manner, thatbetween the moment compensation device and its drive, in accordance withthe present invention, a slip coupling with settable or controllablemoment, for instance a magnet coupling or an induction coupling isdisposed.

It is still another object of the present invention to provide anapparatus for damping of tensile stress fluctuations and for control ofthe web tension on unrolling devices, wherein devices for variation ofthe winding angle of the web about the feeding roller serving as momentcompensation device, for instance, guide rollers swingable about thefeeding roller, are provided, with the assistance of which the windingangle of the web about the moment compensation device, and thereby thefriction moment between the web and the moment compensation device issettable or controllable.

The efi'ect of the last-mentioned device can be advantageously supportedby a blowing ledge, which is swingable jointly with the guide rollers,is disposed in the incoming split between the moment compensation deviceand the web such, that it produces an air pillow between the web and themoment compensation device.

With these and other objects in view, which will become apparent in thefollowing detailed description, the present invention, which is shown byexample only, will be clearly understood in connection with theaccompanying drawing, in which the only FIGURE is a schematic view of anunwinding device with a moment limitation between a moment compensationdevice and its drive.

Referring now to the drawing, the apparatus comprises a roller 1 fromwhich a web 2 is fed by means of a spring-biased roller 3 and a firstfeeding roller 4 serving as a moment compensation device over a dancingroller 5 and by means of a second feeding roller 6 to a working machine(not shown). The feeding rollers 4 and 6 are driven with an equal numberof revolutions in the same rotary direction by means of a driving gear 7with the help of gears 8 and 9. The diameter of the feeding roller 4 isless than 3 percent preferably less than 0.3 percent larger than thediameter of the feeding roller 6, so that the peripheral speed of thefeeding roller 4 is slightly larger, than the peripheral speed of thefeeding roller 6. It is obvious that the larger peripheral speed of thefeeding roller 4 can be obtained also by corresponding drivetransmissions at equal or smaller diameter than the feeding roller 6.

The dancing roller 5 is secured to a two-armed level 12 mounted in alever bearing 11, which lever 12 causes by means of a brake mechanism 13or another transmission device a braking of the roller 1, if the dancingroller 5 is lowered, while the braking is released when the dancingroller 5 is raised. It is to be understood, that by means of the dancingroller 5, not only a core braking of the roller 1, but undercircumstances also a peripheral braking of the roller 1 can be broughtabout.

Between the gear 8 and the feeding roller 4 is arranged a slip couplingI0, the slipping moment of which is adjustable. The function of thiscontrol is as follows:

If the web tension on a first web section between the roller 1 and thefeeding roller 4 serving the moment compensation corresponds with thereference value or nominal value, the expansion of the second websection between the roller I and the feeding roller 4 corresponds alsowith the expansion caused by the load of the web 2 by the dancing roller5 between the feeding roller 4 and the feeding roller 6. In the slipcoupling 10, a slip occurs which corresponds with the peripheral speeddifference between the feeding roller 4 and the feeding roller 6, sothat both feeding rollers rotate with equal peripheral speed.

If the web tension in the first web section increases between the roller1 and the feeding roller 4 up to the slip moment set on the-slipcoupling 10, then also the expansion of the web in this sectionincreases and the expansion difference between nominal expansion and theactual expansion reaches the second web section between the feedingrollers 4 and 6 with a slight reduction of the slip in the slip coupling10. In this second web section, the expansion of the web is equalized,the dancing roller 5 is slightly raised and, thereby, the braking of theroller l is reduced.

If the web tension increases for a short period above the value, whichis preset by the set slip moment of the slip coupling 10 as well as bythe load of the web 2 by the dancing roller 5, then the web 2 is braked,the slip in the slip coupling 10 increases and the dancing roller 5 israised by reducing of the winding due to constant unrolling of the web 2by the feeding roller 6 and the expansion compensation in the windingquickly and, nevertheless, for a small path only, which makessuperfluous the damping of the dancing roller movement, so that thebraking of the roller 1 is quickly reduced. The control is, thereby,completely stable, since first the additional nondamped influence of thedancing roller 5 is lower than the damping influencing of the dancingroller 5 by the expansion compensation, and furthermore, after thereduction of the web tension peak directly and alone the dampenedinfluencing of the dancing roller 5 by the expansion compensationbecomes effective.

By the reduction of the web tension, at first the control over theexpansion effect takes place upon stronger reduction, a faster feedingof the web section fed into the winding is brought about by a reductionof the slip, so that in both cases the dancing roller 5 is lowered andthe braking of the roller 1 is increased. If no web tension is present,for instance, after a quick braking and an emergency braking,respectively, after a web tear or during insertion of a new web, then inaccordance with the laws of rope friction, no friction between thefeeding roller 4 and the web 2 occur and during insertion of a new webwith standing feeding rollers 4 and 6, respectively, the feeding roller4 can, upon engagement of the web with the slip coupling 10, freelyrotate, so that the new web 2 can be inserted without prevention by theroller 4 since it can freely rotate over slip coupling 10 and withoutany particular measures.

Suitable slip couplings can be automatically adjusted or controlled bythe web tension or by other values.

By example, the switching-on of the slip coupling with the switching andcontrol of the driving machine, can be obtained electrically ormechanically.

With the device in accordance with the present invention, it can beassured that the web tension cannot go below and not above the limitvalue determined by the slip moment, without starting an acceleratedcontrol and that the permissible tension limit value can be setselectively by setting of the devices determining the slip.

The slip makes possible a disturbance-free restarting after an emergencybraking, as well as a comfortable and fast insertion of a new web.

While I have disclosed several embodiments of the present invention, itis to be understood, that these embodiments are given by example onlyand not in a limiting sense.

I claim:

1. An apparatus for damping of tensile stress variations and for controlof the web tension on braked unwinding devices for webs of flexiblematerial, as paper, plastic foils, and the like comprising a firstfeeding roller and a second feeding roller,

a roll of web material to be unwound,

a brake means for said roll of web material,

a means for actuating said brake means,

a dancer roller disposed between said first feeding roller and saidsecond feeding roller and connected with said means for actuating saidbrake means,

said first feeding roller being arranged on the side of said roll of webmaterial and serving as a moment compensation device,

said second feeding roller serving as a feeding device for the web,

said web passing from said roll of web material being unwound therefromto said first feeding roller, said dancer roller and said second feedingroller, in that order,

a gear for driving said first and second feeding rollers, and

a slip coupling operatively disposed between said first feeding rollerand said gear.

1. An apparatus for damping of tensile stress variations and for controlof the web tension on braked unwinding devices for webs of flexiblematerial, as paper, plastic foils, and the like, comprising a firstfeeding roller and a second feeding roller, a roll of web material to beunwound, a brake means for said roll of web material, a means foractuating said brake means, a dancer roller disposed between said firstfeeding roller and said second feeding roller and connected with saidmeans for actuating said brake means, said first feeding roller beingarranged on the side of said roll of web material and serving as amoment compensation device, said second feeding roller serving as afeeding device for the web, said web passing from said roll of webmaterial being unwound therefrom to said first feeding roller, saiddancer roller and said second feeding roller, in that order, a gear fordriving said first and second feeding rollers, and a slip couplingoperatively disposed between said first feeding roller and said gear.